1. Field of the Invention
The invention relates to waste water decontamination. For example, one embodiment of the invention relates to a reactor system for and method of maintaining a substantially two-phase (liquid/solid) operating environment within an ozone supersaturated decontamination reactor, thereby maximizing the contact of contaminants with ozone and oxygen particles, while minimizing loss of catalytic material due to turbulence associated with expansion of free ozone and/or oxygen. The invention, however, is not limited to this specific embodiment.
2. Background Art
Ozone-based decontamination of water is known. For instance, U.S. Pat. No. 4,696,739 (hereinafter xe2x80x9cthe ""739 patentxe2x80x9d) discloses a water purification apparatus having multiple countercurrent ozone extraction columns. The apparatus, however, involves a three-way (gas/liquid/solid) reaction vessel. See Col. 2, lines 56-64. The apparatus is designed to bubble the ozone through the liquid. Col. 1, line 51.
The device disclosed in U.S. Pat. No. 3,336,099 (hereinafter xe2x80x9cthe ""099 patentxe2x80x9d) is an apparatus for sanitizing liquids. The ""099 patent apparatus includes baffles, to enhance the gas/liquid contact. However, the ""099 patent apparatus, like the ""739 patent apparatus, permits the ozone/air to bubble in the reactor.
U.S. Pat. No. 5,114,576 discloses a first ozonation of waste water followed by a catalytic decomposition of the remaining ozone before discharge of the cleansed fluid. U.S. Pat. No. 5,116,574 (hereinafter xe2x80x9cthe ""574 patentxe2x80x9d) discloses multiple extraction systems with recycled exhaust gas to increase overall ozone usage efficiency. The ""574 patent also discloses the use of discrete modules to effect a fixed percent improvement for each module.
U.S. Pat. No. 4,007,118 (hereinafter xe2x80x9cthe ""118 patentxe2x80x9d) discloses an apparatus for ozone oxidation of waste water using catalytic media reactors where the granules are contained in a filter bag. The ""118 patent also discloses the use of an upflow, dispersed catalyst bed where the granules are dispersed with ozone-containing gas, while the fines are collected downstream of the dispersed bed and recycled back to the bed. The ""118 patent further discloses operating the catalytic reactors at pressures above atmospheric.
U.S. Pat. No. 5,173,257 discloses the simultaneous use of gaseous ozone and dissolved ozone to sanitize solid particles and react with dissolved contaminants. U.S. Pat. No. 5,190,659 discloses the use of a complex filter/valve apparatus to automate the necessary steps of cleaning, backwashing and reusing an ozone-reactive filter. U.S. Pat. No. 4,898,679 (hereinafter xe2x80x9cthe ""679 patentxe2x80x9d) discloses the use of near freezing temperatures to increase the concentration of ozone in water. In the ""679 patent, the supercharged water is then heated at the point of use and used to disinfect or decontaminate sludge, other contaminated fluids or equipment.
In prior systems, the task of ozonating water and catalytically decomposing the ozone to continue the decontamination has been complicated by the demands of handling a 3-phase system (gas/liquid/solid). Therefore, there exists a need for an apparatus and method capable of performing decontamination substantially in two phases while maximizing ozone concentration.
Investigators Hoigne and Bader originally elucidated a complex, core free-radical mechanism and their work was added to by Peyton and Zappi. Their mechanism dictates that ozone and hydrogen peroxide form hydroxyl free radicals which in turn oxidize the refractory organics or halogenated organics. The hydroxyl radical is formed from a number of sources: (1) from added hydrogen peroxide that is irradiated with UV light and forms radicals directly; (2) from added peroxide that dissociates in water, where the anionic species then becomes a radical; (3) from dissolved ozone that is irradiated with UTV light to become a radical directly; (4) from dissolved ozone that is irradiated with UV light and, with water, becomes hydrogen peroxide and, thereafter, a radical; (5) from dissolved ozone that decays directly into radicals; or (6) from dissolved ozone that is catalytically decomposed into free radicals, through an as yet undefined mechanism.
Each of these mechanisms has a different reaction rates and equilibrium constants. For example, the amount of ionic species available to make radicals is strongly affected by pH. The effective dose of free radicals, those that work to oxidize contaminants is strongly consumed by naturally occurring free radical terminators. Terminators include dissolved bicarbonates, humic and fulvic acids. High doses of hydrogen peroxide also terminate free radical reactions. High doses of radicals also terminate, i.e., self-extinguish, when two radicals collide. The net effective dose is the total dose of radicals less the radicals that terminate.
Hoigne first proposed, and Peyton confirmed, that a radical propagating mechanism exists with available oxygen. If a radical mechanism is initiated, and if the number of initiators exceeds the number of terminators, then the oxygen radical propagation step may occur. Peyton demonstrated this propagation step by bubbling ozone-in-oxygen gas through a batch reactor. Once the radical process was initiated, the ozonator was shut off and the oxygen left on. The rate of substrate removal clean up did not change after the ozone was turned off until the substrate was consumed.
This process approach effectively demonstrated the chemistry of radical chain reactions in a batch reactor. But the continued bubbling of large amounts of gas through a continuous flow reactor stirs and mixes the two fluids, thus destroying any plug flow characteristics in the reactor. Plug flow reactors are the design of choice when oxidizing micro-levels of pollutants down to non-detect levels. It is well understood that it takes three or more stirred reactors in series to simulate the kinetics of a single plug flow reactor. Adding multiple reactors in series to overcome the difference between a stirred reactor and a plug flow reactor adds cost and complexity.
A substantial number of aqueous streams must be treated to meet government laws for release into the environment. Such aqueous streams typically contain one or more impurities, such as suspended solids, dissolved organic matter, microorganisms, dissolved mineral matter and the like. Ozone has been used for decades to remove low concentrations of these contaminants. Historically, ozone has not been used for highly concentrated contaminants because it is difficult to get enough ozone into the water and the capital and energy costs are too high versus competing technologies. For example, ozone is widely used to disinfect drinking water, or to tertiary treat municipal waste, but it is not used to treat water produced from oil and gas recovery because it is cheaper to deep well inject this water. Likewise, the water from making pesticide and herbicide intermediates, which can have a COD (xe2x80x9cChemical Oxygen Demandxe2x80x9d) of 10,000 is hauled off and deep well injected as a hazardous waste because the nitro phenols would otherwise poison the municipal treatment plant. In addition, these high concentration fluids are very sudsy. Using a gas to oxidize the contaminants introduces a problem of stable suds formation pump and consequent cavitation.
Ozone, however, has found use in specific high concentration environments where no other technology will work, such as color removal from non-biodegradable color components in the pulp and paper industry, where it is common to encounter a low sudsing stream because the biodegradable components have already been removed by traditional processes. U.S. Pat. No. 5,397,490 to Dickerson describes a process that provides ozone doses that are 2-4 times the normal solubility of ozone in water per multi-zone treatment at gas-to-liquid ratios of 2:1. Improved results are reported as the dose increases. Unfortunately, the Dickerson process leaves behind increasing amounts of unused ozone as the dose increases. Therefore, there exists a need for a process that can achieve similar ozone doses in the treated water with no unused ozone. Such a process would be inherently less expensive while providing comparable oxidation effectiveness.
Ozone extraction and ozone reactors are well known in the prior art. In general, the art can be divided into two categories: Ozone extraction with integral reactors such as shown as in U.S. Pat. No. 5,173,257 to Pearson and ozone extractors with subsequent reactors in U.S. Pat. No. 5,114,576 to Ditzler, or free radical generators in U.S. Pat. No. 5,302,298, to Leitzke. Both categories are characterized by capture of the exhaust gas and then either venting the gas, drying and recycling the gas, or recycling the gas to an upstream gas recycling (recovery) system. Prior systems also show multiple zones in the extraction process, usually cocurrent and counterflow, but other combinations are also described. All prior systems using multiple extraction zones commingle the exhaust gas from the extractor/reactor and pass the commingled gas to a serially communicating next stage.
When multiple, serially connected extraction zones exist in a given extractor/reactor, one zone has a higher residual ozone gas concentration (after extraction) than the other zone (after extraction). Thus one zone has a relatively higher concentration of residual ozone than in the xe2x80x9caveragexe2x80x9d concentration exhaust gas. xe2x80x9cAveragexe2x80x9d gas is then passed to the next serially connected unit operation.
Prior devices recognize that ozone extraction is not 100% effective, particularly when the ozone dose to be extracted exceeds the natural solubility of ozone in water (about 13 ppm). In these situations, prior devices generally recycle the exhaust gases to a serially connected prior extractor/reactor module (Pearson, Dickerson, Leitzke). In one such device, up to 200 ppm ozone is fed to the reactor where four serially connected extractor/reactor modules are used to extract the ozone. This system still only achieves 71% extraction efficiency.
In other prior systems, LaRaus (""040) uses similar cocurrent then countercurrent extraction zones. Those skilled in the art would follow the process of LaRaus with a free radical inducer zone as in Leitzke (""298) or Ditzler (U.S. Pat. No. 5,114,576). Those skilled in the art will recognize that there is more residual unextracted ozone as the water to be treated gets cleaner as fluid flows serially through the prior art processes because there are fewer substrate molecules remaining to react with available ozone. The present invention is distinguished over LaRaus by how the unentrained gases are handled. LaRaus commingles waste gas from the cocurrent and countercurrent section, thus taking a high ozone-containing gas from one section, commingling that with low concentration gas from a second zone to achieve average, greater than nil, ozoneconcentration gas commingled with exhaust gas. This practice is true of all the early prior art. LaRaus scrubs this ozone-containing, commingled gas in his feed tank and routes his vented exhaust underground. Improvements were made by Leitzke, who also commingles his countercurrent and cocurrent exhaust gases and adds an additional entire module to scrub his exhaust. The double scrubbed gas is then vented, passed through an ozone-destruct unit or dried and recycled to the ozone generator, a very complex series of steps to contend with gas that was not completely extracted. An additional problem with the Leitzke process is that liquid scum must exit through a gas vent, through a water-sensitive catalytic destruct unit or through a drier into a gas compressor in order to exit the system.
Pearson (""257 and ""574) uses only a single cocurrent extractor/reactor in his reaction modules and recognizes the inefficiency inherent in this design, because the design serially connects extractor/reactor modules with a double scrubbing module that has no fresh ozone addition before venting the exhaust from the double scrubbing extractor to an ozone destruct unit to handle any still unextracted ozone.
A further improvement is the process invented by Dickerson. In the Dickerson process, gas is extracted in a cocurrent/countercurrent high pressure loop. The tank is divided into zones where the first zone is the countercurrent extraction zone. The second, lower zone is a combined countercurrent/cocurrent extraction, free radical inducer zone. Dickerson teaches that these zones can be separate tanks or two zones in one tank. Either way, the gases from the two zones are commingled and recycled upstream as in Leitzke. Scum is not well handled in the Dickerson process because expensive, automatic level control valves maintain a liquid level substantially below the top of the tank. This means that scum cannot escape until it builds up sufficiently to rise to the gas outlet line. With sufficient recycle time, scum will migrate sequentially upstream to the first module (with the dirtiest, sudsiest water) and exit through the gas vent line to an undisclosed area.
Clearly there is a need for a process that can extract large absolute quantities of ozone, safely and at substantially 100% efficiency.
When large quantities of gaseous ozone are extracted in water containing, for example, organic molecules, the resulting water is foamy and often times creates a floating blanket of scum. This scum has to be removed from the tops of the extractors. Much of the prior art allows this scum to pass with the exhaust gas back to the feed tank. Other art serially connects the gas and any scum directly to the exhaust system, to a catalytic ozone destruct unit, or directly to a drier and an air compressor. Those skilled in the art recognize that catalytic destruct units are fouled by free moisture, and that free water may not pass the gas dryer stage. The examples described by these practitioners are of low sudsing fluids that do not create scum. There is a particular need to handle internally generated scum as part of a practical process.
In the waste water remediation business, cost is a major consideration. There is a strong need for lower cost processes that are simple to operate, inherently safe and do not require sophisticated operators to run. There is a need for a process that can achieve very high gas transfer per extractor/reactor module and have substantially no free gaseous ozone in the exhaust gas that is serially passed to the next unit operation. A system that used multiple gas extractors in a given extractor/reactor module and did not commingle the exhaust gases from each zone could pass the high concentration ozone exhaust gas to the inlet of the low ozone extraction zone, whereupon the low zone could exhaust substantially ozone-free gas. A system like this would be more efficient and require fewer, serially connected extractor/reactor modules, thus reducing the cost of the equipment substantially. A system like this could be designed to collect and transfer the scum along with the high concentration exhaust gas into the low concentration zone where it can be collected and fed back to the feed tank for subsequent, well known treatment.
It is an object of the present invention to simplify the ozonation/deozonation process by eliminating the excess equipment currently required to handle catalyst fines. It is a further object of the present invention to eliminate automation as practiced in the prior art. It is a further object to eliminate non-reactive filtration systems and their associated maintenance. Another object of the present invention is to eliminate the drawbacks of 3-phase systems from the ozonation/catalytic deozonation process. A further object is to provide an ozonation reactor zone that is substantially free of large, visible gas bubbles.
Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.